Controlled release of water-soluble agents

ABSTRACT

A method of controlled release includes exposing a polymeric composition to an aqueous liquid to permit surface erosion of a polymeric material of the polymeric composition, thereby controllably releasing the at least one water-soluble agent. The polymeric composition includes the polymeric material and the at least one water-soluble agent homogenously mixed with the polymeric material. The polymeric material includes a polyester copolymer of an alcohol monomer and an acid monomer. A method of preparing a polymeric composition includes forming a polymeric material from an alcohol monomer and an acid monomer in the presence of at least one water-soluble agent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/149,732 filed May 9, 2016, allowed, which is a continuation of U.S.application Ser. No. 14/725,654 filed May 29, 2015 and issued as U.S.Pat. No. 9,359,472 on Jun. 7, 2016, which claims the benefit of andpriority to, U.S. Provisional Application No. 62/005,299, filed May 30,2014, and to U.S. Provisional Application No. 62/138,796, filed Mar. 26,2015, all of which are hereby incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates generally to controlled release processes,processes for preparing polymeric compositions, and/or polymericcompositions and more particularly, but not exclusively, where thepolymeric composition includes a water-soluble agent for controlledrelease.

BACKGROUND OF THE INVENTION

Polymers are used extensively in the preparation of biomaterials.Certain biomaterials used in the field include biocompatible and/orbioabsorbable synthetic polymers that are composed of monomers havingdifferent affinities for water. For example, in certain polymers formedfrom glycerol and a diacid, the glycerol may be water soluble while thediacid is nearly insoluble. Thus, when biomaterials including thesecompounds are prepared, the process for such preparation may simplyinclude adding the monomers neatly to a vessel and allowing them toreact directly. Such processes may be problematic because thepolymerization reaction may be difficult to control and modify. Theproducts of such reactions may have inconsistent properties betweenbatches, resulting in biomaterials that may fail to performconsistently.

One such method is described in U.S. Pat. No. 7,722,894, Wang et al. The'894 patent describes a process for creating poly(glycerol sebacate) viaa polycondensation reaction that occurs under a specific identifiedreaction condition, namely an anhydrous polycondensation reactioncarried out at 120° C. and a pressure of 1 Torr or less to yield acolorless elastomer. However, this method and the specific form ofpolymer that results have numerous drawbacks that restrict or preventtheir satisfactory commercial use. Among the drawbacks are that thespecific process conditions taught by the '894 patent do not actuallyyield an elastomer as described, but instead produce a high molecularweight resin. While further curing of this resin outside of the timeperiods described can in course still yield an elastomer, the conditionsof initial polymerization result in a polymer with a high polydispersitythat render it unsuitable for commercial production in certainapplications, such as those requiring tight control over molecularweight distribution, including controlled release.

Due to these and other difficulties present in the field, there is anunmet need for processes of synthesizing polymeric materials, where suchprocesses allow for control and modification of the polymerizationreaction occurring therein. The present invention meets those needs.

BRIEF DESCRIPTION OF THE INVENTION

The present invention meets the needs in the field for tunablepreparations of polymeric materials by providing water-mediatedprocesses for preparing polymeric materials, including articles andbioabsorbable materials that may be prepared by such processes.

In a first aspect, the invention includes a method of preparing apolymeric material. The method includes combining an alcohol monomer andan aqueous solution in a vessel. Methods of the invention may providefor adding an acid monomer to the vessel, then refluxing the alcoholmonomer, the aqueous solution, and the acid monomer in the vessel. Themethod includes removing water from the vessel, such as by distillingwater from the vessel, as necessary. Additionally, the method includesproducing the polymeric material in the vessel. In certain aspects ofthe invention, the polymeric material includes a polyester of thealcohol monomer and the acid monomer.

In another embodiment of the method of the invention, the alcoholmonomer may include glycerol. Further, the aqueous solution may comprisea water-soluble agent. The acid monomer of the invention may include adiacid and, for example, the diacid may include a compound of theformula [HOOC(CH₂)_(n)COOH], where n=1-30. In a particular embodiment,the acid monomer may include malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, ora combination thereof. Particularly, the diacid in the methods of theinvention may be sebacic acid.

In other embodiments of the method of the invention, the steps ofcombining the alcohol monomer and the aqueous solution in the vessel,adding the acid monomer to the vessel, refluxing, distilling, and/orproducing the polymeric material may include the steps of heating,stirring, and/or applying sub-atmospheric pressure as necessary toprepare the desired polymeric material.

In further embodiments of the method of the invention, the method mayinclude adding a supplemental aqueous solution, an oligomer thepolymeric material, and/or a co-monomer to the vessel.

In another aspect, the present invention includes an article ofmanufacture that may be prepared by the processes of the invention. And,in an additional aspect, the present invention includes a bioabsorbablepolymeric material prepared by the water-mediated processes of theinvention, wherein the polymeric material may include a filament, afiber, a yarn, a braid, a knit material, a mesh, a sheet, a coating, atube, or a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary and the following detailed description of theexemplary embodiments of the present invention may be further understoodwhen read in conjunction with the appended drawings, in which:

FIG. 1 schematically illustrates a known prior art method for preparingPGS where the polyol and diacid reactants are added together neatly in avessel.

FIG. 2 illustrates a water-mediated method of preparing a polymericmaterial in accordance with an exemplary embodiment.

FIG. 3 graphically compares the FTIR spectra of PGS polymerizationreactions after 120 minutes in (A) a water-mediated PGS polymerizationreaction; and (B) a standard PGS polymerization reaction.

FIG. 4 graphically compares the FTIR spectra of PGS polymerizationreactions after 76 hours in (A) a standard PGS polymerization reaction;and (B) a water-mediated polymerization.

FIG. 5 graphically compares the FTIR spectra of PGS polymerizationreactions in (A) a standard PGS polymerization reaction at 120 minutes;(B) a low temperature, water-mediated PGS polymerization reaction; and(C) a standard PGS polymerization reaction at 76 hours.

FIG. 6 graphically illustrates GPC chromatograms of PGS polymerizationof water mediated polymerization reactions and a comparative non-watermediated polymerization reaction.

Wherever possible, the same reference numbers will be used throughoutthe drawings to represent the same parts.

DETAILED DESCRIPTION OF THE INVENTION

A significant need exists in the field of biomaterial preparation forprocesses that allow for easier material processing, better early stagereaction control, inclusion of temperature sensitive compounds andinclusion of water-soluble additives in the synthesis of polymericmaterials composed of monomers, which have minimal affinities for water,such as, for example, poly(glycerol sebacate) (PGS).

As demonstrated in FIG. 1, the polymer PGS may be synthesized by addingsolid sebacic acid and liquid glycerol together and reacting them atabout 120° C. for several hours. Sebacic acid has a melting point of133-137° C. This means that the sebacic acid/glycerol mixture mustinitially be heated to temperatures greater than 133° C. to allow thesebacic acid to melt, and the two liquid reactants to be mixed. Themelting of sebacic acid in the presence of glycerol is problematicbecause the reaction then takes place rapidly between the glycerol andthe fraction of melted sebacic acid. Thus, the reaction conditions usedin the art create difficulties in specifying the extent of the reactionas well as in controlling the reaction.

As set forth herein, the addition of water to the mixture before heatingsolves the melting problem by causing the sebacic acid to liquefy at amuch lower temperature (between 100° C. and 105° C.). Additionally,because the reaction between a diacid (e.g., sebacic acid) and analcohol or polyol (e.g., glycerol) is an ester condensation, and aproduct of this reaction is water, the reaction will not progress whilea substantial amount of water is present in the reaction mixture.Indeed, the present disclosure may be contrasted to the prior art, whichis replete with references that expressly recite anhydrous reactionconditions, such as the '894 patent discussed above.

As shown below with respect to the synthesis of poly(glycerol sebacate),water is a reaction product and thus the introduction of additionalwater into a system containing the reactants slows the reactionkinetics.

Once the added water is removed from the reaction, such as bydistillation, the remaining reactants exist in liquid form, and arehomogenously mixed, thus allowing the reaction to proceed in acontrolled manner. Furthermore, because the amount of water added isknown, a more reliable start time for the reaction can be calculatedbased on the measurement of the amount of water removed by distillation.That is, once the water initially added is removed, any additional waterthereafter removed is water resulting as a product of the reaction.

The problems in the field are solved by the present invention, whichincludes methods for preparing polymeric materials, such as theexemplary embodiment illustrated in FIG. 2. The polymeric materials, andbiomaterials that may be prepared therefrom, may be biocompatible and/orbioabsorbable.

The methods of the invention that allow for the preparation of suchpolymeric materials may first include the step of combining an alcoholmonomer and an aqueous liquid in a vessel. In certain aspects of themethods of the invention, a selected alcohol monomer, utilized in thepolymerization of the polymeric material, and the aqueous solution maybe combined or otherwise added together either sequentially orsimultaneously into a vessel. As used herein, the term “polymer” or“polymeric” may include a homopolymer, copolymer, terpolymer,cross-linked polymer or the like. Moreover, the term “alcohol monomer,”may refer to aliphatic alcohols having one or more hydroxy substituentsand may, for example, include polyols having two or more hydroxysubstituents. In certain aspects, the alcohol monomer may be glycerol.

As used herein the term “vessel” may refer to a beaker, bottle,canister, flask, bag, receptacle, tank, vat, jar, vial, tube, and thelike that are generally known in the art to contain fluids or fluid-likematerials and liquids.

The aqueous liquid of the invention may be water alone or be a solutionof water and one or more water-soluble agents. The inclusion of watersoluble agents allows for the incorporation of such agents into thepolymeric material itself, where such agents would be difficult orimpossible to provide without the aid of the present invention. Anythermally labile, water-soluble agents may be employed. Water-solubleagents in accordance with exemplary embodiments may include, forexample, a vitamin, an anti-inflammatory agent, a protein, a protease,an herbicide, an aquarium food source, an anti-mitotic agent, ananti-platelet agent, an anti-coagulant agent, an anti-thrombotic agent,a thrombolytic agent, an enzyme, a chemotherapeutic agent, an antibioticagent, an immunological adjuvant, a natural product, a scaffoldingmaterial, a processing agent, or a combination thereof. Vitamins of theinvention may include water-soluble or non-soluble vitamins known in theart. Preferably, the vitamins of the invention may include vitamin B1,vitamin B2, vitamin B3, vitamin B5, vitamin B6, vitamin B7, vitamin B9,vitamin B12, vitamin C, or a combination thereof.

When water-soluble agents are incorporated or utilized in the process ofthe invention, they are provided in the polymeric material at atherapeutically effective amount and may be employed in pure form or,where such forms exist, in pharmaceutically acceptable salt, ester, orprodrug form. As used herein, the phrase “therapeutically effectiveamount” of the water-soluble agents of the invention means a sufficientamount of the agents as therapeutics in the treatment of a disorder, ata reasonable benefit/risk ratio applicable to any medical treatment.

The step of combining the alcohol monomer and the aqueous solution maytake place at room temperature in the vessel or may include heating ofthe alcohol monomer and the aqueous solution to a temperature of about50 to 200° C. In certain embodiments, the step of combining the alcoholmonomer and the aqueous solution may include heating the alcohol monomerand the aqueous solution to a temperature of about 80 to 150° C. or,preferably, about 90 to about 110° C. Additionally, the alcohol monomerand the aqueous solution after combination may be heated for about 5minutes to about 240 minutes, or about 30 minutes to about 180 minutes,or for a time sufficient to dissolve or homogenously disperse thealcohol monomer in the aqueous solution.

After the alcohol monomer and aqueous solution are combined in thevessel, an acid monomer may be added to the vessel and mixed with thealcohol monomer and aqueous solution. The acid monomer may be addedneatly (i.e., without being dispersed or dissolved in solvent) to thevessel or may be added as a solution or mixture in a selected solvent.The acid monomer of the invention may include acidic compounds havingone or more acid substituents including, but not limited to, monoacids,diacids, triacids, tetraacids, and the like. In certain aspects of theinvention, the acid monomer is a diacid. Regarding diacids of theinvention, such diacids may have the formula [HOOC(CH₂)_(n)COOH],wherein n=1-30. Preferably, the diacid of the invention may includemalonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid,suberic acid, azelaic acid, or sebacic acid. Particularly, the diacid ofthe invention is sebacic acid. In certain aspects, the alcohol monomer,acid monomer, and aqueous solution (e.g., water) may be provided in amolar ratio of about 0.5-5 mol alcohol monomer:0.5-5 mol acidmonomer:0.5-5 mol water, with the alcohol monomer and acid monomerpreferably present to achieve a molar equivalent of alcohol and diacidmonomers. In a particular aspect, sebacic acid, glycerol, and water maybe combined in molar ratio of about 1-2 mol sebacic acid, 1-2 molglycerol, and 2-5 mol water.

Following addition of an acid monomer to the vessel, the contents of thevessel (e.g., alcohol monomer, aqueous solution, and acid monomer) maythen be refluxed by heating the vessel. Refluxing the contents of thevessel provides, for example, melting of the acid monomer where the acidmonomer is a solid. Indeed, an exemplary process may begin by addingwater to the reaction mixture of glycerol and sebacic acid, therebyreducing the mixture's overall viscosity. This allows the mixture to bestirred easily. The water provides efficient heat transfer betweenreaction vessel walls and solid acid monomer (e.g., sebacic acid),allowing the acid monomer to melt quickly and form a dispersion. Forexample, sebacic acid is slightly soluble in water at room temperature,and this solubility is increased as the temperature increases. Thesuspension or colloidal mixture interaction further facilitatesefficient liquefaction of the solid acid monomer. Moreover, the presenceof the water in the mixture impedes the reaction of, for example,glycerol and sebacic acid, thus allowing all reactants to be molten andhomogenous before the water is removed and the reaction substantiallycommences.

The step of refluxing the contents of the vessel may also includeproviding a condenser to the vessel in order to preserve the volume ofsolvent (e.g., water) contained within the vessel. Refluxing thecontents of the vessel may include heating the contents to a temperatureof about 50 to 200° C. or about 80 to 150° C. Preferably, the contentsof the vessel are heated to a temperature of about 100 to 140° C.Additionally, the alcohol monomer, aqueous solution, and acid monomermay be heated for a selected period of time, which may include a periodof about 1 to 336 hours or, more particularly, about 24 to 48 hours.Alternatively, where the acid monomer is a liquid or oil at roomtemperature, the step of refluxing may be avoided. It will further beappreciated that in some embodiments, the vessel may be pressurized toreach temperatures up to 200° C. or higher to shorten the time underreflux and/or for use in melting diacids that remain solid at hightemperatures that could not otherwise be readily achieved.

After refluxing the contents of the vessel to achieve melting andthorough mixing of the reactants, the water added to the vessel torender that achievement is removed, such as through distillation or anyprocess known in the art. The remaining reactants exist in liquid form,and are homogenously mixed, thus allowing the reaction to proceed in acontrolled manner, which includes the production of additional water asa reaction by-product. That is, some of the water present in the vesseland subsequently removed is a result of its inclusion in the aqueoussolution while some is present as the byproduct of the condensationreaction. By measuring the amount of water removed, it can be determinedwhen the included water has all been removed, which gives a general ideaof when the reaction shifts back toward the production of product,meaning that all reactants come to the reaction at the same time.

The step of distilling the water from the vessel may include heating thevessel to a temperature of about 50 to 200° C. or, particularly, about80 to 150° C. In a particular aspect, the step of distilling the waterfrom the vessel may include heating the vessel to a temperature of about110 to 140° C., such as about 115° C., 120° C., 125° C., or 130° C. orany temperature or range of temperatures therebetween, although vacuumdistillation at lower temperatures is also contemplated.

Following the distillation of the added water from the vessel, thealcohol and acid monomers can readily react and polymerize forming thepolymeric material. Thus, the polymeric material is thereby produceddirectly from the vessel to yield the final product. Typically,producing the polymer material includes two separate steps after theadded water is removed involving first heating under an inert gasfollowed by heating under application of vacuum, in which water ofreaction is distilled from the vessel. Heating the contents of thevessel in these two steps (inert gas purge and vacuum) may be at thesame or different temperatures from one another. The temperature mayrange from about 50° C. to about 200° C. or, particularly, about 80° C.to about 150° C. In a particular aspect of the invention, the contentsof the vessel may be heated to a temperature of about 100° C. to 140°C., such as about 115° C. to about 135° C., such as about 115° C., 120°C., 125° C., 130° C. or 135° C. or any temperature or range oftemperatures therebetween.

Regarding the heating of the vessel and/or the contents of the vessel inany of the process steps described herein, the heating of the vesseland/or its contents may be performed by conductive heating, convectiveheating, radiative heating, or a combination thereof. With respect toradiative heating, the vessel and/or its contents may be heated with,for example, microwave radiation and/or infrared radiation.

The distillation may occur in conjunction with stirring and/or purgingthe contents of the vessel by reaction under an inert gas, such asfollowing an initial distillation step after reflux to remove the wateradded as a processing aide. As used herein, the term “inert gas” mayrefer to nitrogen, carbon dioxide, a noble gas, or a combinationthereof. For example, noble gases of the invention may include helium,neon, argon, and the like. In certain aspects, the inert gas isnitrogen. The process of the invention may include purging the contentsof the vessel with an inert gas at a rate of about 1 mL/min to about 10L/min, such as while heating in the range of temperatures previouslydescribed. Moreover, inert gas purging of the vessel may be provided fora period of about 1 minute to about 48 hours or, more particularly, forabout 1 hour to about 24 hours and preferably is conducted atatmospheric pressure, although carrying out this step at higher or lowerpressures is contemplated.

Distillation may include heating and/or applying sub-atmosphericpressure to the vessel, and in particular distillation to remove waterof reaction following the inert gas purge step of producing takes placethrough the application of a vacuum. For instance, distilling mayinclude connecting a source of sub-atmospheric pressure to the vesselaccording to any process known in the art (e.g., a fluidic connection ofa peristaltic pump, diaphragm pump, rotary pump, etc.). Sub-atmosphericpressure may be applied to the vessel at a pressure of less than about760 Torr or, particularly, at a pressure of about 40 mTorr to 50 Torr.In another aspect, sub-atmospheric pressure may be applied to the vesselat a pressure of about 5 to 20 Torr, such as about 10 Torr.

Additionally, the sub-atmospheric pressure may be applied to the vesselat a constant pressure for a selected period of time or thesub-atmospheric pressure may be varied during the course of itsapplication. For example, the application of subatmospheric pressure mayinclude a stepwise reduction from a first pressure to a second pressure,such as a first pressure less than about 760 Torr and the secondpressure greater than about 40 mTorr, particularly, greater than 1 Torr.

The distillation of water from the vessel may include heating and/orapplying sub-atmospheric pressure to the vessel for a selected period oftime. For example, the heating and/or application of sub-atmosphericpressure to the vessel may be applied for about 1 hour to 336 hours or,more particularly, about 12 hours to 168 hours. In a particular aspect,the heating and/or application of sub-atmospheric pressure to the vesselmay be applied such as about 24, about 25 hours, about 26 hours, about27 hours, up to about 48 hours, or any time or range of timestherebetween.

In another aspect, the reactants (e.g., the alcohol and acid monomers)may be allowed to react under the application of sub-atmosphericpressure in addition to, or instead of, heating the reactants. Indeed,sub-atmospheric pressure may be applied to the vessel at a pressure ofless than about 760 Torr or, particularly, at a pressure of about 40mTorr to 50 Torr. In another aspect, sub-atmospheric pressure may beapplied to the vessel at a pressure of about 1 to 50 Torr, such as 5 to20 Torr, such as about 10 Torr. The polymerization of the alcohol andacid monomers may continue (with or without heating and/or applyingsub-atmospheric pressure) for about 1 hour to 336 hours or,particularly, about 12 hours to 168 hours. In a particular aspect, thepolymerization (i.e., production of the polymeric material) may continuefor about 24 to 120 hours, including about 24 hours, about 25 hours,about 26 hours, about 27 hours, up to about 48 hours, up to about 76hours, or any time or range of times therebetween.

Upon completion of the polymerization reaction to produce the polymericmaterial, the resulting polymeric material, which may be in the form ofa moldable, pliable resin, is removed from the vessel and stored asnecessary or required. Additionally, completion or progress of theprocesses of the invention may be determined by any means known in theart including, but not limited to, FTIR, DCS, SEC, TGA, LCMS, and/orNMR. Among the advantages are that the resulting product is resin thatcan be subsequently processed and then cured into any size, shape to anylevel of cross-linking as may be desired for a particular application orcan be used in the resin form without any appreciable cross-linking foruse, for example, as a coating.

In another aspect, a supplemental aqueous solution may optionally beprovided to the vessel during the course of the process. For example,the supplemental aqueous solution may be added during the refluxingstep, initial distillation step, and/or producing step while thereactants are left to polymerize into the polymeric material. Thesupplemental aqueous solution may include additional agents that may beincorporated into the resulting polymeric material. For example, agentsthat may be heat sensitive may be provided at a later stage in thereaction after some polymerization has taken place. The supplementalaqueous solution of the invention may include a vitamin, ananti-inflammatory agent, a protein, a protease, an herbicide, anaquarium food source, a growth factor, a glycoprotein, a proteoglycan,an anti-mitotic agent, an anti-platelet agent, an anticoagulant agent,an anti-thrombotic agent, a thrombolytic agent, an enzyme, achemotherapeutic agent, an antibiotic agent, an immunological adjuvant,a natural product, a scaffolding material, a processing agent, or acombination thereof. As used herein, the term “scaffolding agents” mayinclude, but is not limited to hydroxyapatite, chitosan, collagen, analginate, polysaccharide, glycosaminoglycan, or a combination thereof.Moreover, as used herein, a “processing agent” of the invention mayinclude, but is not limited to an agent for preparing a putty, an agentfor preparing a dispersion, a surfactant, a dye, a pigment, a bio-activematerial, a non-bio-active material (e.g., a non-bio-active meshcoating), a brightening agent, or a combination thereof.

Without being confined to any one theory of the invention, it isbelieved that in the early stages of the reaction, oligomeric fractionsare formed, and in later stages of the reaction, these oligomericfractions are polymerized together. In the example of sebacic acid, theacid melts between 133° C. and 137° C., but the oligomeric fractionsmelt at much lower temperatures (about 45° C.). For example, once moltenand mixed with glycerol, the sebacic acid/glycerol mixture may staymolten above 115° C. Thus, elevated temperatures may be necessary forthe beginning of the reaction, but when oligomeric fractions are formed,the reaction continues at much lower temperatures. In certain aspects ofthe invention, oligomers of PGS (OGS) may be prepared by either methodsof the present invention or other methods known in the art, and may beadded during the method of the invention. Thus, it will be appreciatedthat in some embodiments, the process may be stopped at a time such thatthe polymeric material formed is still in the form of oligomericfractions.

Indeed, an extension of these findings indicates that the oligomericfractions may be synthesized, then brought to lower temperatures (e.g.,about 60° C.). To these oligomers, an aqueous solution or supplementalaqueous solution that includes additional agents for incorporation intothe polymeric material that may be thermally unstable above thistemperature can be added while mixing. Sub-atmospheric pressure can thenbe applied to remove the added water provided by the aqueous solutionafter the additive is homogenously dispersed, and the reaction cancontinue to completion at the lower temperature.

Furthermore, additional monomers or even polymers may be utilized in theinvention and added to the vessel during at least one of the refluxing,distilling, and producing steps to form polymeric materials composed ofthree or more monomers. Additional co-monomers may include a diacid, asdefined above, or may include other monomeric units known in the artsuch as lactic acid, glycolic acid, caprolactone, hexamethylenediisocyanate, methylene diphenyl diisocyanate, and the like. Inalternative aspects of the invention, PGS or other polymers formed inaccordance with exemplary embodiments described herein may besubsequently reacted with other polymers such as poly(lactic acid), byway of example only. These polymers may be added at any stage during orafter completion of the initial polymerization reaction, such as afterthe inert gas step but before vacuum, during vacuum, or even after theinitial polymeric material has been formed and removed from the vesselin a separate reaction.

In some embodiments employing PGS, the co-polymers demonstrate anincrease in the elasticity over neat PGS, while also decreasing thetensile modulus and tackiness of the material. A PGS/PLA copolymer doesnot require a secondary treatment to become elastomeric and also has alower surface energy than neat PGS, resulting in the ability to coathydrophobic substrates such as silicone, PTFE and polypropylene.

Another advantage of the copolymer compositions is the additionalcontrol afforded to the degradation kinetics and subsequent releasekinetics of the composition. PGS is a surface eroding polymer while PLAis a bulk eroding polymer. Both mechanisms result in varied degradationkinetics which ultimately control the mechanical properties and releasekinetics over the degradation time of the material. Depending on the enduse of the material the co-polymer composition can be tailored toprovide the appropriate degradation profile.

Any desired ratio may be employed; in one embodiment, a copolymer havinga molar ratio of 90% PGS to 10% PLA or other co-polymer/co-monomer isprovided. In another embodiment, the ratio is 50/50. Any other desiredratio may also be employed, such as any ratio in which theco-polymer/co-monomer content is less than 90:10, greater than 10:90,such as greater than 50:50, or any points in between.

Moreover, monofunctional or polyfunctional compounds may be added to thevessel during the method of the invention. For example, monofunctionalor polyfunctional compounds may be added during at least one of therefluxing, distilling, and producing steps to enable modification of thesurface energy properties of the polymeric material produced by themethods of the invention. A “monofunctional compound” of the inventionmay include, for example, an organic compound having one functionality,which may be a carboxyl, ester, amide, hydroxyl, epoxide, carbonate,amine, ester, carbamate, urea, carbonyl, sulphonamide, and the like. A“polyfunctional compound” of the invention may include, for example, anorganic compound having two or more functionalities selected from thegroup consisting of carboxyl, ester, amide, hydroxyl, epoxide,carbonate, amine, ester, carbamate, urea, carbonyl, sulphonamide, orcombinations thereof. Depending on the number and type of such compoundsused in the methods described herein, surface energy properties of theresulting polymeric material may be modified in a controlled manner.

The process of the invention may include stirring the contents of thevessel at a rate of about 1-1000 RPM or, more particularly, at a rate ofabout 100-500 RPM. Indeed, the process of the invention includes mixingthe acid and alcohol monomers (e.g., sebacic acid and glycerol) bystirring the mixture under high shear to facilitate the mixing of solidacid monomers and liquid alcohol monomers. Additionally, by adding waterto the reaction mixture, the amount of shear necessary to stir isgreatly reduced. For example, stirring the reactants is possible priorto melting the sebacic acid, for example, if water is present, but isimpossible until the sebacic acid is molten in the absence of water.Earlier stirring is preferable because it allows for more thoroughmixing of the reactants, which allows for a more consistent product.

An additional advantage of stirring reactants in combination with watermediation is that the vessel contents are essentially isothermal,resulting in better thermal management compared to a standardpolymerization process in which heat at the walls is greater than at thecenter of the reactor while at elevated temperature as the sebacic acidstarts to melt, exacerbating the problems with the standard process asthe reaction proceeds to form large molecular weight polymers at thetank walls while the reactants at the center form smaller molecularweight fractions.

Water mediation has also been observed to impact particle size in thepolymer resin which in turn may affect the resin'sblending/copolymerization characteristics, solubility, and coatingcharacteristics, or a combination thereof, among others. In particular,water mediated methods in accordance with exemplary embodiments evidencesmaller particle size and a narrower distribution over conventionalmethods of synthesis. Particle size may impact the degradation rate,cross-link density, drug-loading capacity, mechanical properties or acombination thereof in any thermoset elastomer formed from the resin.For example, among the advantages are that a narrower distribution meansthat degradation time of the elastomer within the body can be betterapproximated. As a result, the thermoset elastomer can more reliably beused for controlled release of active ingredients incorporated duringinitial formation.

In some embodiments, PGS homopolymeric material formed in accordancewith exemplary embodiments of the invention have a weight averagemolecular weight of less than 20,000 g/mol, such as less than about15,000 g/mol. Some exemplary embodiments have a polydispersity index ofless than 7.5, such as less than about 7 and in some embodiments, about6.5 or lower. In other embodiments, such as PGS/PLA copolymers, forexample, the weight average molecular weight achieved through exemplaryembodiments may be up to 130,000 g/mol or higher.

According to the process of the invention, a bioabsorbable orbiocompatible polymeric material may be manufactured. The bioabsorbablepolymeric material may further comprise a filament, a fiber, a yarn, abraid, a knit material, a mesh, a sheet, a coating, a tube, or acombination thereof. In a particular aspect, the polymeric materialincludes poly(glycerol sebacate) that may or may not incorporate avitamin, an anti-inflammatory agent, a protein, a protease, anherbicide, an aquarium food source, a growth factor, a glycoprotein, aproteoglycan, an antimitotic agent, an anti-platelet agent, ananti-coagulant agent, an anti-thrombotic agent, a thrombolytic agent, anenzyme, a chemotherapeutic agent, an antibiotic agent, an immunologicaladjuvant, a natural product, a scaffolding material, a processing agent,or a combination thereof.

In another embodiment of the invention, the processes disclosed hereinmay be used to prepare emulsions of the polymeric material for 3Dprinting. For example, an emulsion of PGS may serve as a bio-ink thatmay be printed onto a substrate using a 3D printer. For example, thepolymeric materials of the invention may include scaffolding materials(e.g., hydroxyapatite) to allow for the preparation of a bio-ink thatmay be printed to bone using a 3D printer as known in the art.

The foregoing processes provide specific advantages over the prior art.For example, it is advantageous to be able to introduce water solubleadditives to the reaction mixtures at different stages because it allowsfor options in doping the polymeric materials produced by the presentprocess. For example, PGS is a water immiscible polymer, so watersoluble additives such as common active pharmaceutical ingredients,therapeutic biological agents, and processing aids would be verydifficult to effectively and homogenously disperse throughout thereactant mixture. However, by providing the present process thatincludes the use of water or aqueous solutions, the water solublemolecules that can be added may be homogenously mixed into the reactantmatrix, forming a dispersion once the water is removed.

The present invention provides distinct advantages in the field byallowing for the controlled preparation of polymeric materials that maybe prepared with consistency between batches. Moreover, by utilizingwater as a medium prior to the commencement of the reaction, thepolymerization between alcohol and diacid may be initiated at lowertemperatures as compared to the reaction between alcohol and diacidbeing performed neat in the absence of an aqueous solvent. Utilizingthese methods in the presence of an aqueous medium rather than anon-aqueous or organic solvent system also provides other distinctadvantages. For example, the use of organic solvents generally reducesthe boiling point of the process and may hinder the miscibility ofcertain reactants, such as limitations on water soluble activeingredients. Residual organic solvents may also have safety andregulatory concerns, whereas water does not share the same health orsafety issues. Additionally, when scaling up such polymerizationreactions that might ordinarily be performed neat, the present processallows for a drop in mixture viscosity due to the presence of waterwhere, ordinarily, the viscosity of a neat polymerization would renderthe reaction difficult or nearly impossible to stir.

The addition of water to the reaction mixture may stall the reactionuntil the water is removed to allow for homogenous mixing of thereactants. Regarding PGS specifically, PGS may be degraded to itsreactant species by the addition of water. Any PGS that may have beensynthesized would ordinarily be degraded. Accordingly, in mostpreparations involving PGS, water is expressly eliminated from all partsof the reaction. An inert gas, such as nitrogen gas, may be used topurge the reaction system, with the application of sub-atmosphericpressure, to remove trace water produced by the condensation from thereaction. However, the approach described herein demonstrates that watermay be used as a processing aid in the preparation of polymericmaterials, such as the polyester PGS, without degradation.

Exemplary embodiments are also directed to biocompatible, bioresorbable,bioabsorbable, and/or biodegradable polymers formed according to one ormore of the methods disclosed herein that include a uniform orsubstantially uniform morphology, molecular weight distribution,molecular weight fraction, monomer distribution, and/or degree ofpolymerization. For example, in one embodiment, the water mediatedsynthesis reduces or eliminates reaction of the acid and alcoholmonomers until after distillation, which increases a uniformity ofreaction throughout the vessel as compared to non-water mediatedmethods. In another embodiment, the increased uniformity of reactionreduces or eliminates different reaction rates and/or lengths throughoutthe vessel, forming the polymer having increased uniformity as comparedto polymers formed through non-water mediated methods.

The uniformity of the polymer formed through water mediated synthesisfacilitates a controlled release of active agents from the polymer, suchas antimicrobial agents. In one embodiment, the controlled release isadjusted through manipulation of the polymerization conditions of themethod. For example, adjusting the reaction temperature, pressure,and/or duration during one or more steps in the method modifies thefinished polymer/oligomer structure, providing control of the releasekinetics. The modifications to the finished structure include, but arenot limited to, modifications in morphology, molecular weight fractions,molecular weight distribution, fraction composition, and/or a degree ofpolymerization of the finished product. These modifications may vary therelease kinetics of the antimicrobial article formed therefrom by, forexample, modifying the release rate, modifying a size of the fractionsreleased during degradation, modifying a porosity of the antimicrobialarticle, modifying a fraction composition of the antimicrobial article,or a combination thereof.

The antimicrobial agents include any component or compound havingantimicrobial properties. Suitable antimicrobial agents include, but arenot limited to, additives dispersed in the polymer, additivesincorporated into the polymer as well as monomers of the polymer andportions of the polymer released during degradation, or somecombinations thereof. For example, one antimicrobial article includespoly(glycerol sebacate) (PGS) itself, the monomers and/or oligomers ofwhich provide antimicrobial properties upon release. Anotherantimicrobial article includes a non-toxic antimicrobial agent derivedfrom human metabolites and provided in biodegradable polymeric form.Without wishing to be bound by theory, it is believed that the sebacicacid and/or glycerol monomers of PGS provide the antimicrobialproperties through quorum quenching or quorum sensing inhibition (QSI).The QSI of the PGS monomers disrupts the quorum sensing of microbialorganisms, such as bacteria, resulting in the microbial organismsremaining in a non-virulent state and/or preventing differentiation intoa pathogenic colony. Although described herein primarily with regard towater mediated synthesis, as will be understood by those skilled in theart, the antimicrobial properties of the polymers, such as PGS, are notdependent upon any specific formation process. Rather, the PGS and itsrepeating units and/or monomers will retain the antimicrobial propertiesdisclosed herein.

Additionally or alternatively, the polymer formed according to one ormore of the methods disclosed herein includes additives that provideand/or increase the QSI of the antimicrobial article. Suitable additivesinclude, but are not limited to, reactable Tween® products (commerciallyavailable from Sigma-Aldrich®); quorum sensing molecules and/or analogsof quorum sensing molecules such as, but not limited to, cis-2-decenoicacid, cis-2-dodecenoic acid, cis-11-methyl-dodecenoic acid, 12methyl-tetradecanoic acid, cis-9-ocatdecanoic acid, tetradecanoic acid,linoleic acid, oleic acid, palmitic acid, stearic acid, lauric acid,myristic acid, sapienic acid, cis-8-octadecenoic acid,cis-11-methyl-2-dodecenoic acid, 4,5-dihydroxy-2,3-dipentadione, cyclicadenosine monophosphates, alarmones (ppGpp and pppGpp), cyclic di-GMP,N-acyl homoserine lactones, diketopiperazines, 4-quinlones(2-heptyl-3-hydroxy-4-quinlone and 2-heptyl-4(1H)-quinolone),phenazines; anti-microbial cations such as Cu, Mn, Ag, Au; orcombinations thereof.

One or more of the antimicrobial agents disclosed herein may be selectedto provide a polymer that is biocidal, eukaryotic non-toxic, deliversprokaryotic antimicrobial activity, or a combination thereof. Inaddition, the composition of the polymer, including one or more of theantimicrobial agents, may be easily modified to reduce or eliminatemicrobial resistance. Furthermore, the composition may be modified toprovide a release fraction directed towards a specific species (e.g.,“targeted antagonism”).

In one embodiment, the antimicrobial agent is polymerized into or onto apolymer backbone and/or otherwise incorporated into the polymer matrixof the antimicrobial article. In another embodiment, the polymerizationof the antimicrobial agent produces a cleavable linkage throughhydrolysis, enzymatic action, and/or pH changes. In a furtherembodiment, the acid monomer, such as the diacid monomer sebacic acid,forms a hydrophilic matrix and/or provides a chemistry that facilitatessurface erosion. The surface erosion properties may provide thecontrolled release of the antimicrobial agents and/or active moiety atthe surface without affecting bulk properties of the antimicrobialarticle or a burst release. Additionally, the polymerization and/orincorporation of the antimicrobial agent in the antimicrobial articlereduces or eliminates migration and/or blooming of the antimicrobialagent, providing uniform or substantially uniform release, chemicalstability, environmental stability, uniform or substantially uniformprotection on conformal surfaces, or a combination thereof.

A polymerization profile of the polymer formed according to one or moreembodiments disclosed herein may provide a continuum of polymeric formsfrom oligomeric gels to thermoset elastomers/polymers. Additionally, thedegree of polymerization of the antimicrobial article formed accordingto one or more embodiments disclosed herein may be varied to produce anyresinous polymer form from a gel through a thermoplastic and which canfurther be processed into a thermoset. Furthermore, the polymer may beincorporated into a composition of matter, such as, but not limited to,an adhesive, coating, polymer blend, extrudate, additive filler, orcombination thereof. For example, a PGS resin formed through watermediated synthesis, as described in one or more of the embodimentsdisclosed herein may, be formulated into a coating and applied to animplantable textile.

The following examples describe the invention in further detail. Theseexamples are provided for illustrative purposes only, and should in noway be considered as limiting the invention.

Comparative Example 1

Glycerol (62.0 g, 0.670 mol) and sebacic acid (135.2 g, 0.670 mol) wereadded to a reactor vessel that was fitted with a chilled water condenserin a distillation setup. A nitrogen purge was applied at 5 L/min. Thereactor vessel was then heated in a melt step at a mantle temperature of140° C. in order to sufficiently melt the solid sebacic acid for 70minutes. The temperature in the reactor was then reduced to 130° C. in astir step and stirred at 500 RPM for 50 minutes.

After the melt and stir steps of the reaction, the reaction continuedfor an additional 24 hours at 120° C. and stirred at 500 RPM undernitrogen (5 L/min).

Next, a vacuum setup was connected to the distillation condenser andsubatmospheric pressure was applied to the contents of the vessel. Thepressure was reduced slowly and step wise (approximately 10-15% perstep) over about 85 minutes to approximately 20 Torr.

Once the pressure in the reaction vessel reached approximately 20 Torr,the vacuum pump was set to 5 Torr. Following the application of vacuum,the reaction vessel was left to react for 1440 minutes at 120° C., andstirred at 500 RPM, with a sub-atmospheric pressure of approximately 5Torr.

Upon removal of water from the reaction mixture, stir speed was reducedto 200 RPM to account for the increased viscosity of the mixture.However, the reaction was allowed to continue to react at a temperatureof 120° C., with the vacuum set at 5 Torr, and stir speed of 200 RPM foran additional 1440 minutes as a PGS polymerization step.

After this period, the PGS material in the reactor vessel wastransferred to a glass jar and allowed to cool on the bench top forabout 45 minutes, then was transferred to a freezer for storage, whereit was frozen for at least about 24 hours before testing and analysis.

Comparative Example 2

In another comparative example, a polymer was made using the method ofsynthesis disclosed in the '894 patent in which equimolar amounts ofglycerol and sebacic acid were reacted at 120° C. (using nitrogeninstead of argon as the inert gas) for 24 hours, followed by reducingthe pressure from 1 Torr to 40 mTorr over 5 hours and then maintainingthe reaction at 120° C. for another 48 hours. This procedure yielded apliable resin, not an elastomer as taught in the '894 patent.

Example 1

Glycerol (62.0 g, 0.673 mol) was added to a reactor vessel with water(37.5 g, 2.08 mol) under stirring. After dissolution of the glycerol,sebacic acid (138.0 g, 0.682 mol) was added to the reactor vessel. Thereactor vessel was then fitted with a condenser to reflux water duringthe melt and stir steps of the PGS polymerization (condenser temperaturewas set to 2.5° C.). The reactor vessel was then heated to a mantletemperature of 140° C. with a stir speed of 500 RPM for approximately 70minutes. The material in the vessel became clear once the reactor vesselreached approximately 95° C.

After the sebacic acid melted, the zone temperature was set to 130° C.and the mixture was stirred at 500 RPM under reflux for 50 minutes.

The condenser was then removed and the vessel was fitted with adistillation condenser to remove water from the vessel. A nitrogen purgewas applied to the vessel (5 L/min) and the zone temperature was set to120° C. During the distillation, the contents of the vessel were stirredat 500 RPM for 1440 minutes.

Next, a vacuum setup was connected to the distillation condenser and thesubatmospheric pressure was applied to the contents of the vessel. Thepressure was reduced slowly and step wise (approximately 10-15% perstep) over about 85 minutes to approximately 20 Torr.

Once the pressure in the reaction vessel reached approximately 20 Torr,the vacuum pump was set to 5 Torr. Following the application of vacuum,the reaction vessel was left to react for 1440 minutes at 120° C., andstirred at 500 RPM, with the sub-atmospheric pressure set to 5 Torr.

Upon removal of water from the reaction mixture, stir speed was reducedto 200 RPM to account for the increased viscosity of the mixture.However, the reaction was allowed to continue to react at a temperatureof 120° C. at pressure of approximately 5 Torr, and stir speed of 200RPM for an additional 1440 minutes as a PGS polymerization step.

After this period, the PGS material in the reactor vessel wastransferred to a glass jar and allowed to cool on the bench top forabout 45 minutes, then was transferred to a freezer for storage, whereit was frozen for at least about 24 hours before testing and analysis.

Example 2

To assess the impact of adding water to PGS pre-polymer following theearly stages of polymerization, further reaction conditions attemperatures below 120° C. were assessed for processability of thematerial.

PGS pre-polymer was produced in three reactor vessels in the mannerdescribed with respect to Example 1, the pre-polymer being that materialafter the nitrogen purge but prior to vacuum. Following these steps,water was added to reactor vessels, and pre-polymer and water were mixedfor approximately 30 min, during which a homogenous dispersion wasformed. Following this step, the condensers were removed from reactorvessels and a vacuum setup was applied. The vacuum was applied to eachreactor, starting at 650 Torr and, slowly, the pressure was reducedstepwise (about 10% each step) to a terminal setting of 5 Torr over thecourse of 100 minutes.

As vacuum reached its terminal setting, the temperature was reduced inreactor 1 to 110° C. and stirred at 500 RPM. The temperature in reactor3 was reduced to 80° C.

Following the application of terminal vacuum, the reactions in reactors1, 2, and 3 were allowed to continue as set forth in Table 1.

TABLE 1 Reactor Temp Stirring Rate Time Vacuum Reactor (° C.) (RPM)(min) (Torr) 1 110 500 1440 <10 2 120 500 1440 <10 3 80 500 1440 <10

Following the steps set forth in Table 1, the stir speed was lowered to200 RPM and the reaction continued in each reactor for another 1440minutes using the same temperature, stirring, and vacuum settings.Finally, the material from each vessel was recovered and stored in glassjars. The jars were allowed to cool to room temperature for 1 hour onthe bench top, then placed in freezer for at least 24 hours prior to anyanalysis.

This example illustrates that water can be added to the moltenpre-polymer and homogenously mixed. Then, the reaction could becontinued using reaction temperatures that were lower than the standard120° C. This allows for compounds, agents, or other reagents to be addedto the reactant mixture, while polymerization continues under mildreaction conditions.

Example 3

Glycerol and sebacic acid were added in 1:1 molar amounts in water tomelt the sebacic acid in a similar manner as described in Example 1using a condenser to reflux water during the melt and stir steps,followed by distillation to remove the water once the sebacic acid wasmelted. The components of the vessel were stirred under nitrogen for 24hours at 120° C. at atmospheric pressure and a nitrogen flow rate of 5 Lper minute, the time measured from the point at which it was determinedall water initially added had been removed by distillation. At theconclusion of that 24 hours, the pressure was reduced to 10 Torr and thetemperature to 115° C., and the reaction was allowed to proceed foranother 24 hours.

Example 4

A water mediated preparation of PGS was carried out by adding glyceroland sebacic acid to water in which the experiment was carried out ingenerally the same manner as Example 3, except that the temperature ofthe mixture during the 24 hour nitrogen purge step was maintained at125° C. instead of 120° C. before the pressure reduced to 10 Torr andthe temperature reduced to 115° C., upon which the reaction was allowedto proceed for another 24 hours.

Example 5

A water mediated preparation of PGS was carried out by adding glyceroland sebacic acid to water in which the experiment was carried out ingenerally the same manner as Example 3 with the reactants purged undernitrogen for 24 hours at 120° C. at atmospheric pressure and a nitrogenflow rate of 5 L per minute, the time measured from the point at whichit was determined all water initially added had been removed bydistillation, except that in this example, that was followed by 26 hoursat a reduced pressure of 10 Torr and a temperature of 130° C.

The examples and comparative examples, along with various intermediates(in which some samples of pre-polymer were obtained after the nitrogenpurge but before the low-pressure step) were characterized throughvarious tests including Differential Scanning calorimetry (DSC),Thermogravimetric Analysis (TGA), Fourier Transform Infrared (FTIR)Spectroscopy, Rheometry Analysis, a titration to determine the acidnumber of the PGS material, as well as gel permeation chromatography(GPC).

For DSC, the calorimeter was loaded with a sample of PGS and tested from−40° C. to 60° C. at 10° C./min, with 1 minute holds.

Focusing on the crystallization temperature (T_(C)) and first melttemperature (T_(M)) of second heat step revealed that samples onlyexposed to water during the melt and stir steps had results typical ofComparative Example 1 (T_(C)≈−11.4° C., T_(M) about 9.5° C.) anddemonstrated that by mediating the reaction with water, the reaction isslowed. Samples reacted at lower temperatures, such as in Example 2 hadresults (T_(C)≈−8.3° C., T_(M) about 12.5° C.) that were intermediate topre-polymer PGS (T_(C)≈−7.4° C., T_(M) about 14.3° C.) and ComparativeExample 1(T_(C)≈−11.8° C., T_(M) about 8.3° C.), which indicated that byreacting at lower temperatures, the reaction is slowed but continues toprogress.

TGA: A sample of Example 1 was loaded into the thermogravimetric systemwith a program set to: (1) hold at 25° C. for 1 minute; (2) ramp to 375°C. at 25° C./min, with a nitrogen purge; (3) ramp to 475° C. at 10°C./min, with a nitrogen purge; and (4) ramp to 550° C. at 10° C./min,with an air purge. The TGA results are consistent with results obtainedthrough analysis of Comparative Example 1 (onset at about 420° C.). Theperiod of water mediation was determined not to affect decompositiontemperature. The TGA results of Example 2 samples (onset at 415° C.) areslightly depressed compared with Comparative Example 1. These resultsdid not show a decomposition occurring at a lower temperature(onset=about 220° C.) indicating that no reactants were present; a lowerdecomposition step is typically present in pre-polymer PGS samples.

FTIR: A sample of Example 1 was analyzed by FTIR-ATR with 32 scans at a4 cm-1 resolution, across the range of 4000-650 cm-1. FIG. 3 shows FTIRspectra of Comparative Example 1 (dashed) and Example 1 (solid) reactantmixtures at 120 min following reaction commencement. FIG. 4 shows FTIRspectra of Comparative Example 1 (dashed) and Example 1 (solid) reactantmixtures at the conclusion of the PGS reaction (i.e., at the end of thefull 48 hour reaction process). FIG. 5 shows FTIR spectra of Example 2(solid) with Comparative Example 1 after 120 min (dark dashed) and 76hours (light dashed) following reaction commencement. Spectra showingrowth of ester carbonyl peak at 1735 cm⁻¹ compared to pre-polymer(120 min) and Comparative Example 1 material.

Rheology: An amplitude sweep and frequency sweep study was performed onExample 1 samples that were molded into a thin layer on aluminum pans,then stored in the freezer for about 24 hours prior to testing. Theflattened samples were placed on the rheometer in flat slabs, while thegap was set to minimize FN on the sample while loading it onto therheometer. All samples (amplitude sweep and frequency sweep) wereallowed to relax in the rheometer hood at 25° C. for at least 10 minutesbefore analysis.

The molten sample rotational flow curve at 80° C. show results thatillustrate small changes in PGS material when the reaction is mediatedwith water. Samples that are mediated only during the melt and stirsteps show viscosities that are at or slightly lower than ComparativeExample 1 (3.8 Pa-s (water-mediated) vs. 4.0 Pa-s (standard non-watermediated).

Similar tests were carried out on Example 2 material with the rotationalflow curve at 80° C. revealing a viscosity intermediate to pre-polymerPGS and Comparative Example 1. (<1.0 Pa-s (pre-polymer PGS); 1.2 Pa-s(Example 2); 4.0 Pa-s (Comparative Example 1)).

Acid Number Analysis: Samples of the PGS were weighted into 50 mLbeakers. Approximately 10 mL of isopropyl alcohol (IPA) was added toeach beaker. The beakers were then covered with paraffin film, thensonicated for 10 minutes. Then, 4 drops of p-naphthol benzein solutionwere added to each beaker, including a 10 mL IPA blank. All samples werethen titrated to a uniform green color using an IPA/KOH titrant.

GPC analysis was conducted to evaluate molecular weight and to calculatepolydispersity index. FIG. 6 graphically illustrates the results ofExamples 1 and 5 along with Comparative Examples 1 and 2.

Molecular weight (Weight Average), polydispersity index (weight averagemolecular weight divided by number average molecular weight), and acidnumber are summarized below in Table 2.

TABLE 2 Molecular Polydispersity Acid Number Weight Index (mg/g) Example1 14663 7.3 42.8 Example 5 12474 6.4 42.7 Comparative Example 1 167718.2 43.0 Comparative Example 2 29306 13.1 37.8

Among the conclusions that can be drawn from the GPC results are thatwater mediation results in achieving a lower molecular weight polymerand a lower polydispersity index that enable easier processing of thepolymeric resin prior to any cross-linking.

Example 6

A low molecular weight (oligomeric) PLA (having a molecular weightdetermined by GPC of −893 g/mol) was created by melt condensationreaction of L-(+)-lactic acid at 150° C. with stirring. The reaction wasconducted for 120 min under a 5 L/min N₂ purge, followed by 120 min at97 torr, then 240 min at 30 torr.

A low molecular weight (oligomeric) PGS (having a weight averagemolecular weight determined by GPC of −5336 g/mol) was formed by meltpolycondensation reaction of equimolar amounts glycerol and sebacic acidat 120° C. with stirring at 24 hrs under a 5 L/min N₂ purge followed by24 hrs of stirring at 10 torr.

The two oligomeric components were mixed (90:10 PGS:PLA molar ratio) ina reaction vessel at 120° C. and 10 torr with stirring for about 19hours. The resulting polymer, a viscous liquid, was then tested againstneat PGS resin. Molecular weights (weight average) as determined by GPCwere about 28,986 for the copolymer and about 12,453 for the PGS.

The copolymer was observed to be more elastic, less stiff and lesssticky and had better recovery than the neat PGS. Differential scanningcalorimetry (DSC) demonstrated the T_(C) of the experimental copolymerswas about −23° C. compared to about −12° C. for the neat PGS, whilerotational melt flow rheology and amplitude sweep rheology bothdemonstrated that the copolymer exhibited more liquid-likecharacteristics than the neat PGS.

Samples of the oligomeric PGS/PLA copolymer and the neat PGS polymerwhere also thermoset by further processing at 120° C. and 10 torr for 72hours. The resulting thermosets were tested for peak load, strain atbreak, and modulus, the results of which are shown below in Table 3.

TABLE 3 oligomeric PGS/PLA neat PGS copolymer Peak Load (N) 3.0 2.5Strain at Break (%) 19 27 Modulus (MPa) 3.9 1.4

Example 7

The PLA of Example 6 was used and mixed with a PGS prepolymer (having aweight average molecular weight determined by GPC of ˜2252 g/mol) thatwas formed by melt polycondensation reaction of equimolar amountsglycerol and sebacic acid at 120° C. with stirring at 24 hrs under a 5L/min N₂ purge. The two components were mixed (90:10 PGS:PLA molarratio) in a reaction vessel at 120° C. and 10 torr with stirring forabout 24 hours. The resulting polymer was a low viscosity liquid thatwas then thermoset at 120° C. and 10 torr for 72 hours and comparedagainst neat PGS as shown in Table 4. Molecular weight (weight average)as determined by GPC was about 10,853 for the copolymer.

TABLE 4 PGS prepolymer/PLA neat PGS copolymer Peak Load (N) 3.0 1.5Strain at Break (%) 19 26 Modulus (MPa) 3.9 0.83

Examples 8 and 9

Examples 8 and 9 were made in the same manner as Examples 6 and 7,respectively, but were instead combined at 5:5 molar ratios; molecularweights (weight average) as determined by GPC were about 129,720 forExample 8 and 16,340 for Example 9.

DSC analysis showed that Examples 6 and 7 demonstrated asemi-crystalline structure while Examples 8 and 9 were amorphous innature.

Examples 10-12

Water mediated preparations of low and high molecular weight PGS(Examples 10 and 11, respectively) were prepared in accordance with theembodiments described herein and subjected to antimicrobial testingfollowing the method described in JIS Z2801:2000 Antimicrobialproperties—Test for antimicrobial activity and efficacy; AMD No.1-2006/05/20. In addition, a PGS resin made in accordance with the watermediated preparations described herein was further processed into athermoset (Example 12) and was also tested under the same methodology.All three samples exhibited antimicrobial activity values of >99%against both Escherichia coli and Staphylococcus aureus.

A number of patent and non-patent publications may be cited herein inorder to describe the state of the art to which this invention pertains.The entire disclosure of each of these publications is incorporated byreference herein.

While certain embodiments of the present invention have been describedand/or exemplified above, various other embodiments will be apparent tothose skilled in the art from the foregoing disclosure. The presentinvention is, therefore, not limited to the particular embodimentsdescribed and/or exemplified, but is capable of considerable variationand modification without departure from the scope and spirit of theappended claims.

Moreover, as used herein, the term “about” means that dimensions, sizes,formulations, parameters, shapes and other quantities andcharacteristics are not and need not be exact, but may be approximateand/or larger or smaller, as desired, reflecting tolerances, conversionfactors, rounding off, measurement error and the like, and other factorsknown to those of skill in the art. In general, a dimension, size,formulation, parameter, shape or other quantity or characteristic is“about” or “approximate” whether or not expressly stated to be such. Itis noted that embodiments of very different sizes, shapes and dimensionsmay employ the described arrangements.

Furthermore, the transitional terms “comprising”, “consistingessentially of” and “consisting of”, when used in the appended claims,in original and amended form, define the claim scope with respect towhat unrecited additional claim elements or steps, if any, are excludedfrom the scope of the claim(s). The term “comprising” is intended to beinclusive or open-ended and does not exclude any additional, unrecitedelement, method, step or material. The term “consisting of” excludes anyelement, step or material other than those specified in the claim and,in the latter instance, impurities ordinary associated with thespecified material(s). The term “consisting essentially of” limits thescope of a claim to the specified elements, steps or material(s) andthose that do not materially affect the basic and novelcharacteristic(s) of the claimed invention. All materials and methodsdescribed herein that embody the present invention can, in alternateembodiments, be more specifically defined by any of the transitionalterms “comprising,” “consisting essentially of,” and consisting of.”

What is claimed is:
 1. A method of controlled release of at least onewater-soluble agent, the method comprising: exposing a polymericcomposition to an aqueous liquid to permit surface erosion of apolymeric material of the polymeric composition, thereby controllablyreleasing the at least one water-soluble agent; wherein the polymericcomposition comprises the polymeric material and the at least onewater-soluble agent homogenously mixed with the polymeric material; andwherein the polymeric material comprises a polyester copolymer of analcohol monomer and an acid monomer.
 2. The method of claim 1, whereinthe water-soluble agent is selected from the group consisting of avitamin, an anti-inflammatory agent, a protein, a protease, anherbicide, an aquarium food source, a growth factor, a glycoprotein, aproteoglycan, an anti-mitotic agent, an antiplatelet agent, ananti-coagulant agent, an anti-thrombotic agent, a thrombolytic agent, anenzyme, a chemotherapeutic agent, an antibiotic agent, an immunologicaladjuvant, a natural product, a scaffolding material, a processing agent,and combinations thereof.
 3. The method of claim 1, wherein the alcoholmonomer comprises glycerol.
 4. The method of claim 1, wherein the acidmonomer comprises a diacid.
 5. The method of claim 4, wherein the diacidcomprises a compound of the formula [HOOC(CH₂)_(n)COOH], wherein N=1 to30.
 6. The method of claim 4, wherein the diacid is selected from thegroup consisting of malonic acid, succinic acid, glutaric acid, adipicacid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and acombination thereof.
 7. The method of claim 6, wherein the diacid issebacic acid.
 8. The method of claim 1, wherein the alcohol monomercomprises glycerol and the acid monomer comprises sebacic acid.
 9. Themethod of claim 1, wherein the polymeric composition further comprisesan antimicrobial agent selected from the group consisting ofcis-2-decenoic acid, cis-2-dodecenoic acid, cis-11-methyl-dodecenoicacid, 12 methyl-tetradecanoic acid, cis-9-ocatdecanoic acid,tetradecanoic acid, linoleic acid, oleic acid, palmitic acid, stearicacid, lauric acid, myristic acid, sapienic acid, cis-8-octadecenoicacid, cis-11-methyl-2-dodecenoic acid, 4,5-dihydroxy-2,3-dipentadione,cyclic adenosine monophosphates, alarmones (ppGpp and pppGpp), cyclicdi-GMP, N-acyl homoserine lactones, diketopiperazines, 4-quinlones(2-heptyl-3-hydroxy-4-quinlone and 2-heptyl-4(1H)-quinolone),phenazines; Cu cations, Mn cations, Ag cations, Au cations, andcombinations thereof.
 10. A method of preparing a polymeric composition,the method comprising: forming a polymeric material from an alcoholmonomer and an acid monomer in the presence of at least onewater-soluble agent such that the polymeric composition comprises thepolymeric material and the at least one water-soluble agenthomogeneously mixed with the polymeric material; wherein the polymericmaterial comprises a polyester copolymer of the alcohol monomer and theacid monomer.
 11. The method of claim 10, wherein the water-solubleagent is selected from the group consisting of a vitamin, ananti-inflammatory agent, a protein, a protease, an herbicide, anaquarium food source, a growth factor, a glycoprotein, a proteoglycan,an anti-mitotic agent, an antiplatelet agent, an anti-coagulant agent,an anti-thrombotic agent, a thrombolytic agent, an enzyme, achemotherapeutic agent, an antibiotic agent, an immunological adjuvant,a natural product, a scaffolding material, a processing agent, andcombinations thereof.
 12. The method of claim 10, wherein the alcoholmonomer comprises glycerol.
 13. The method of claim 10, wherein the acidmonomer comprises a diacid.
 14. The method of claim 13, wherein thediacid is sebacic acid.
 15. The method of claim 10, wherein the alcoholmonomer comprises glycerol and the acid monomer comprises sebacic acid.16. The method of claim 10, wherein the forming incorporates at least aportion of the at least one water-soluble agent into the polymericmaterial.
 17. A polymeric composition comprising a polymeric materialand at least one water-soluble agent homogenously mixed with thepolymeric material, wherein the polymeric material comprises a polyestercopolymer of an alcohol monomer and an acid monomer.
 18. The polymericcomposition of claim 17, wherein the water-soluble agent is selectedfrom the group consisting of a vitamin, an anti-inflammatory agent, aprotein, a protease, an herbicide, an aquarium food source, a growthfactor, a glycoprotein, a proteoglycan, an anti-mitotic agent, anantiplatelet agent, an anti-coagulant agent, an anti-thrombotic agent, athrombolytic agent, an enzyme, a chemotherapeutic agent, an antibioticagent, an immunological adjuvant, a natural product, a scaffoldingmaterial, a processing agent, and combinations thereof.
 19. Thepolymeric composition of claim 17, wherein the alcohol monomer comprisesglycerol.
 20. The polymeric composition of claim 17, wherein the acidmonomer comprises a diacid.